Abstract:

The present invention discloses two new related substances (6) and (7) of
Anastrozole synthesis from Q.A. Salt (5) as in Scheme-1 and purification
procedures to get Anastrozole (1) free from (6) and (7).

7. A compound consisting essentially of Anastrozole, the compound prepared
by a process comprising the steps ofa. dissolving Anastrozole in an
alcoholic solvent;b. adding hydrocarbon to the alcoholic solution; andc.
isolating pure Anastrozole,in which the impurity content of related
substances of structures (6) & (7) is less than 0.1% ##STR00006##

8. The compound of claim 7, wherein the hydrocarbons added to the
alcoholic solution are anti-solvent and are selected from a group
consisting of aromatic hydrocarbons, and aliphatic hydrocarbons.

9. The compound of claim 8, wherein the hydrocarbons are selected from a
group consisting of C1-C10, straight chain, branched and cyclic
hydrocarbons.

Description:

FIELD OF INVENTION

[0001]Aromatase is an enzyme, which effects aromatisation of ring A in the
metabolic formation of various steroid hormones. Various cancers, for
example, breast cancer are dependent upon circulating steroid hormones,
which have an aromatic ring A. Such cancers can be treated by removing
the source of ring A aromatised steroid hormones, for example, by the
combination of oophorectomy and adrenalectomy. An alternative way of
obtaining the same effect is by administering a chemical compound, which
inhibits the aromatisation of the steroid ring A.

[0002]Anastrozole is a non-steroidal antineoplastic, claimed to inhibit
the aromatase (oestrogen synthase) activity. It is useful in the
treatment of advanced breast cancer in postmenopausal women.

BACKGROUND OF INVENTION

[0003]Synthesis of Anastrozole is reported in U.S. Pat. No. 4,935,437 and
European Patent Application EP 0,296,749. The synthetic route mentioned
in the said patents suffers a major disadvantage of the formation of
Anastrozole regioisomer (2).

##STR00001##

[0004]To overcome the formation of regioisomer (2), another synthetic
route is reported in U.S. Pat. No. 4,935,437; in which compound (3) is
reacted with 4-amino-1,2,4-triazole (4) to form quaternary ammonium salt
(5), which further undergoes diazotisation reaction to give Anastrozole
(1) free from regioisomeric impurity (2) (Scheme-1).

##STR00002##

[0005]It has been observed that the cyano groups undergo hydrolysis in
various conditions to form hydrolysed related compounds.

OBJECTS OF THE INVENTION

[0006]It is an object of the present invention to provide an improved
process for the preparation of pure Anastrozole (1) free from impurities
arising due to hydrolysis of cyano groups during the course of the
preparation of Anastrozole (1).

DESCRIPTION OF INVENTION

[0007]Intermediate (3) undergoes condensation with 4-amino-1,2,4-triazole
(4) in a suitable solvent to give
4-amino-1-[3,5-bis-(1-cyano-1-methylethy)phenzyl]-1H-[1,2,4]triazolium
bromide (Q.A.-salt) (5) in good yield.

[0008]It has been further observed that during the preparation of
Anastrozole, hydrolysis of cyano groups also takes place leading to the
formation of two major related substances. The hydrolysis products formed
due to hydrolysis are characterized as
2-[3-(cyanodimethyl-methyl)-5-[1,2,4]triazol-1-ylmethyl-phenyl]-isobutyra-
mide (6) and
2-[3-(1-carbamoyl-1-methylethyl)-5-[1,2,4]triazol-1-ylmethylphenyl]-isobu-
tyramide (7). Both the substances are isolated and well characterized by
using NMR and mass analysis. The 1H-NMR, 13C-NMR and mass
analysis of the isolated products
2-[3-(cyanodimethyl-methyl)-5-[1,2,4]triazol-1-ylmethyl-phenyl]-isobutyra-
mide (6) and
2-[3-(1-carbamoyl-1-methylethyl)-5-[1,2,4]triazol-1-ylmethylphenyl]-isobu-
tyramide (7) are in accordance with the chemical structure. 1H-NMR of
compound (6) shows three singlets at δ 7.4, 7.3 and 7.24 for three
protons in aromatic ring, and two protons at δ 6.95 for amide
group. However four methyl groups appear at δ 1.65 and 1.41, each
for six protons. The 13C-NMR of compound (6) shows a quaternary peak
at δ 177.4 for amide carbonyl carbon, three tertiary aromatic
carbons at δ 125.0, 122.7 and 122.2; two aliphatic quaternary
carbons at δ 52.1 and 46.1 and two peaks for methyl carbons at
δ 28.4 and 26.7. Further, the structure is also confirmed by the
mass analysis of compound (6).

[0009]The 1H-NMR of compound (7) shows peaks at δ 6.86 for amide
protons and its 13C-NMR shows amide carbonyl carbon at δ 179.6.
Further, the structure is also confirmed by the mass analysis of compound
(7).

[0010]The HPLC chromatogram of Anastrozole shows presence of related
substances (6) and (7) in 0.02% to 1.0% in crude product which are
removed by the repeated crystallization using an alcoholic solvent with a
mixture of hydrocarbon as anti-solvent.

[0011]The removal of the related substances
2-[3-(cyanodimethyl-methyl)-5-[1,2,4]triazol-1-ylmethyl-phenyl]-isobutyra-
mide (6) and
2-[3-(1-carbamoyl-1-methylethyl)-5-[1,2,4]triazol-1-ylmethylphenyl]-isobu-
tyramide (7) are accomplished by the crystallization method using various
solvent systems to get Anastrozole in its purer form. Thus, the main
embodiment of the present invention relates to the products
2-[3-(cyanodimethyl-methyl)-5-[1,2,4]triazol-1-ylmethyl-phenyl]-isobutyra-
mide (6) and
2-[3-(1-carbamoyl-1-methylethyl)-5-[1,2,4]triazol-1-ylmethylphenyl]-isobu-
tyramide (7) as related substances in Anastrozole. According to another
embodiment, the present invention also relates to the process for the
preparation of Anastrozole with related substances
2-[3-(cyanodimethyl-methyl)-5-[1,2,4]triazol-1-ylmethyl-phenyl]-isobutyra-
mide (6) and
2-[3-(1-carbamoyl-1-methylethyl)-5-[1,2,4]triazol-1-ylmethylphenyl]-isobu-
tyramide (7) preferably, less than 1.0%, more preferably, 0.1% and most
preferably, below quantitation limits.

[0012]Following the procedures as per Scheme-1 Anastrozole is obtained in
its purer form but still some extent of the related substances
2-[3-(cyanodimethyl-methyl)-5-[1,2,4]triazol-1-ylmethyl-phenyl]-isobutyra-
mide (6) and
2-[3-(1-carbamoyl-1-methylethyl)-5-[1,2,4]triazol-1-ylmethylphenyl]-isobu-
tyramide (7) still remain contaminating Anastrozole, which is further
purified using organic solvents preferably isopropanol, ethyl acetate or
mixture of solvents preferably cyclohexane/ethyl acetate,
cyclohexane/isopropanol or a mixture of solvents with water. Thus another
embodiment of the present invention relates to the process for the
preparation of Anastrozole free from related substances (6) and (7) by
crystallization of crude Anastrozole using alcohols preferably selected
from C1 to C10 alcohols and hydrocarbons, preferably selected from
aliphatic hydrocarbons preferably C1 to C10.

[0013]4-Amino-1-[3,5-bis-(1-cyano-1-methylethyl)benzyl]-1H-[1,2,4]triazoli-
um bromide (5) (70 g) was dissolved in conc. HCl (280 mL) in a 5 L R.B.
flask and cooled to -5 ° C. A solution of sodium nitrite (15 g) in
water (70 mL) was slowly added to the reaction mixture at 0-5° C.
in 4 hrs and the reaction mixture was stirred for one hour at 0-5°
C. and further at 10-20° C. for next 3 hours. The reaction mixture
was quenched by the addition of a solution of urea (4.5 g) in water (15
mL). Toluene (700 mL) was added to the reaction mixture and the
heterogeneous solution was further cooled down to 0-5° C. The
solution was basified by the addition of liquor ammonia (365 mL) slowly
in 4 hours at 5-25° C. Organic layer was separated and further
washed with water (200 mL). Aqueous layer was removed and a solution of
cone. HCl (140 mL) in water (140 mL) was added to the organic layer
slowly in 30 minutes at 25-30° C. and reaction mass was heated at
60-65° C. for 30 minutes. The lower aqueous layer (280-300 mL),
containing product was collected in a conical flask maintaining at
50° C. The aqueous part was again washed with toluene (700 mL) at
60-65° C. for 30 minutes. The lower aqueous layer, containing
product was charged in a separating funnel and again washed with fresh
toluene (700 mL). The aqueous layer, containing product was transferred
in a R.B. flask and ethyl acetate (350 mL) was added to it. The
heterogeneous solution was cooled to 0-5° C. basified by the slow
addition of liquor ammonia (280 mL) in 2-3 hours at 5-25° C. The
solution was stirred for one hour at 25-35° C., and the upper
organic layer (360-375 mL), containing product was separated and filtered
through hyflow super cell bed. Solvent was distilled out below 50°
C. under vacuum leaving approximately 100 mL ethyl acetate in the flask.
The content of the flask was cooled down to 25-35° C. and
cyclohexane (500 mL) was added to the solution slowly in 30 minutes. The
precipitated solid product was filtered and washed with fresh cyclohexane
(20 mL×2). The product was dried at 45-50° C. to get crude
Anastrozole (44 g) with more than 98% HPLC purity contaminated with
related substance (6) as 0.36% and with related substance (7) as 0.05%.

EXAMPLE-2

Removal of Related Substances (6) and (7) from Anastrozole

[0014]Anastrozole (33 g) from example-2 was dissolved in isopropanol (100
mL) at 45-50° C. The solution was cooled down to 25-35° C.
and cyclohexane (100 mL) was added drop wise in 30 minutes. The solution
was stirred at 25-35° C. for 2 hours; the precipitated solid
product was filtered and washed with fresh cyclohexane (30 mL×2)
and dried at 50° C. to get 23 g of pure Anastrozole contaminated
with related substance (6) as 0.09% and with related substance (7) below
detection limit.

EXAMPLE-3

Purification of Anastrozole

[0015]Pure Anastrozole (11 g) from Example-2 was further purified by
dissolving in isopropanol (33 mL) at 45-50° C. The solution was
cooled down to 25-35° C. and cyclohexane (33 mL) was added drop
wise in 30 minutes. The solution was stirred at 25-35° C. for 2
hours; the precipitated solid product was filtered and washed with fresh
cyclohexane (30 mL×2) and dried at 50° C. to get 8.9 g of
pure Anastrozole containing with 0.03% of (6) as related substance and
another related substance (7) below detection limit. Related substance
(6) can be further removed below detection limit by repeating the same
process.